1. Field of the Invention
This invention relates to upgrading petroleum naphtha. It more particularly refers to a modified reforming process for more efficiently increasing the octane number of the produced reformate at a smaller yield loss as compared to conventional reforming.
2. Description of the Prior Art
The reforming of petroleum naphthas in order to increase their octane number is one of the most important and widely practiced unit processes in the petroleum industry. Reforming catalysts are usually noble metals, such as platinum, or mixtures of metals, on acidic supports such as alumina. The acidity of reforming catalysts is often improved by chloriding them and/or by incorporating zeolites with them. The term reforming is used in the petroleum industry to embrace a number of hydrocarbon transformations which occur more or less simultaneously or sequentially including: dehydrogenation of naphthenes to aromatics, isomerization of aliphatics and aromatics, and dehydrocyclization of aliphatics. These reactions are cumulatively endothermic and, therefore, it is conventional to carry out reforming in a multiple series of reactors with initial and interstage heating. Thus, the initial naphtha feed is heated to a suitable reforming temperature of at least about 900.degree. F. pressurized with hydrogen to some suitable pressure of at least about 150 psig and fed into contact with reforming catalyst in a first stage reactor. Passage of the charge through the reactor converts portions of it, according to at least some of the reaction mechanisms listed above, to an intermediate product having a lower temperature below about 825.degree. F., a higher aromatics content and an associated higher octane. This intermediate improved product is then, in its entirety, heated in a furnace to a suitable temperature of at least about 900.degree. F. and then passed through a second stage reactor containing reforming catalyst in which the above-recited reactions or some of them go forward endothermically to produce a further improved, intermediate product having a lower temperature, but not as low as the first stage reactor and a higher aromatics content and, therefore, a higher octane number. A third, and perhaps even a fourth, stage reactor with intermediate heating is conventionally employed to produce a final reformate of substantially higher octane than the feed naphtha. As reforming proceeds, the octane number of the liquid increases and the volume thereof decreases. Reforming with a given catalyst and at a given severity has a characteristic yield-octane relationship such that as the octane of the reformate is pushed higher, the volume thereof decreases. This yield-octane relationship is not a straight line function but is progressive in the sense that as the absolute octane is increased, the incremental octane improvement is achieved at the expense of proportionally increasing yield loss. That is, there is a greater yield loss in going from 95 to 96 octane than there is in going from 88 to 89.
In the recent past, there was impetus to improve the efficiency of naphtha octane upgrading, including a reforming process, by obtaining the final incremental octane boosts by processes other than noble metal reforming as described above. Thus, various processes have been proposed for upgrading reformate by shape selectivety cracking out the very low octane components using an erionite or a ZSM-5 type zeolite catalyst. Processes have also been proposed for combinations of shape selective cracking of the lowest octane components of reformate coupled with alkylation of aromatics in the reformate by at least some of the cracked fragments. Other proposals have suggested combination configurations whereby the naphtha was first subjected to shape selective cracking of the lowest octane components, followed by reforming, followed by another shape selective cracking operation. Another proposal has been to upgrade reformate by sequential shape selective cracking of the lowest octane components with respectively an erionite type and a ZSM-5 type catalyst.
While all of these processes have been more or less successful in increasing the reformate octane number at some yield sacrifice smaller than that which would have been necessary by increased severity reforming to the same octane level, all of them suffer from one or more associated disadvantages such as the problem of adjusting the temperature of the reformate product to that required to support shape selective cracking of the lowest octane components of the reformate.
Of particular importance is U.S. Pat. No. 3,729,409, Chen, which discloses the generic combination of reforming and reformate upgrading over a ZSM-5 zeolite catalyst.
It is, therefore, an object of this invention to provide a novel process configuration for upgrading the octane number of naphthas.
It is another object of this invention to provide a novel modified reforming process.
It is a further object of this invention to upgrade the octane number of naphthas at a reduced yield loss.
Other and additional objects of this invention will become apparent from a consideration of this entire specification including the claims hereof.